1. Field of the Invention
This invention relates to flame-retardant compositions and more particularly relates to such compositions comprising normally flammable organic polymers and novel halogenated organic flame retardants.
2. Description of the Prior Art
It is known that halogenated compounds are sometimes useful for imparting flame retardancy to normally flammable organic polymers. However, the halogenated compounds which have been proposed for use as flame retardants usually have one or more of the following disadvantages: volatility, instability at processing temperatures, incompatibility, inefficiency, and toxicity.
If the halogenated compound is too volatile, it does not remain in the polymer to function as a flame retardant when needed. If it is unstable at processing temperatures, it decomposes to cause corrosion of the equipment and discoloration of the polymer. If it is incompatible with the polymer, it exudes to the surface to form an esthetically unpleasing deposit, the removal of which results in removing the flame retardancy which the compound was supposed to impart. If it is inefficient, it must be used in such high concentrations that it has an unduly deleterious effect on polymer properties and unduly increases the cost of the fabricated polymer. If it is toxic, it presents more-or-less serious hazards to the health and/or life of fabricators and users of the flame-retardant composition in which it is used and also presents an ecological problem when the fabricated polymer is discarded.
Since some of these disadvantages make a compound less than desirable for use as a flame retardant, and others actually prevent it from having any practical utility as a flame retardant, it is apparent that there is a need for a flame retardant which is substantially non-volatile, stable at processing temperatures, compatible, efficient, and non-toxic.
It is believed that the general lack of success of the prior art in producing such a flame retardant is at least partially due to the tendency of a given factor to degrade at least one of these properties while improving another. For instance, it has been found that compounds containing cycloaliphatic bromine are sometimes more efficient than other halogenated compounds, but these compounds have poor stability at processing temperatures and frequently have other disadvantages, such as volatility, incompatibility, and toxicity. Compounds containing vinylic bromine on the ring carbon atoms are more stable but less efficient, and they may also be too volatile, toxic, and incompatible.
It might be thought that the toxicity of halogenated compounds could be reduced by decreasing their halogen contents, but this has not been found to be the case. Comparison of halogenated insecticides having similar structures indicates that toxicity does not simply increase with an increase in halogen content and, in fact, may even decrease with an increase in halogen content. For instance, the hexachlorocyclopentadiene adduct Aldrin, with six chlorine atoms, has a halogen content of about 58% and an LD.sub.50 number of 55; the hexachlorocyclopentadiene adduct Heptachlor, with seven chlorine atoms, has a halogen content of about 66% and an LD.sub.50 number of 130-135; the hexachlorocyclopentadiene adduct Chlordane, with eight chlorine atoms, has a halogen content of about 69% and an LD.sub.50 number of 570.